The present invention relates to a device in a sewing machine with a connecting link for setting the stitch width or the stitch length.
The basic principle of zigzag control by means of a link and of stitch displacement by a shift of the zero point at the link fulcrum is apparent from Renter's "The Sewing Machine Specialist," Vol. III, Pages 14 and 15.
Thus, devices for setting the stitch width are conventional. They comprise in most cases a linear or curved connecting link exhibiting on one side a guide track for a sliding block, designed as an open groove, and on the other side thereof the bearing permitting a pendulum motion of the connecting link. In devices of this type serving for setting the stitch width, the connecting link suspension is adjustable in correspondence with the desired stitch area position (left-center-right). The connecting link can be driven, for example, by way of an eccentric or a cam disk while the sliding block can transmit its movement via a tie rod to the needle bar frame. The connecting link of such a setting device must be manufactured and supported with extreme accuracy, since any inaccuracies that may exist will have a direct effect on the sewing result. Therefore, it has been suggested to manufacture the connecting link and the sliding block of a synthetic resin for the purpose of reducing not only the manufacturing costs but also the mass to be moved. However, the unilateral support of the connecting link still has remained a disadvantage, leading also in the case where the connecting link is made of a synthetic resin, to distortions due to a correspondingly asymmetrical application of force.
Therefore, the present invention is based on the object of providing a device of the type discussed above wherein this disadvantage is eliminated, and the bearing of the connecting link and the guidance of the sliding block are selected so that the force of transmission takes place in the plane of symmetry of the connecting line, and lateral forces leading to distortions are avoided.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The device of the present invention is characterized in that the connecting link is a flat member, the end portion of this member on the bearing side being disposed in a bearing head which in turn is pivotably supported on a support by means of two trunnions arranged symmetrically to the central plane of the flat member and extending away at right angles to the flat sides of this flat member. The sliding block is fashioned as a sliding sleeve displaceably guided on the flat member and encompassing the latter.
Since, on the one hand, the connecting link is bilaterally supported and, on the other hand, the sliding block encompasses the connecting link on all sides, the force input at the connecting link bearing, just as the force output by the sliding block, occur in the center plane of the connecting link designed as a flat member, so that it is practically impossible for lateral forces to arise, which would lead to distortions.
In an especially advantageous embodiment, the connecting link consists of a flat member of metal, for example steel or aluminum, advantageously produced by stamping, whereas the bearing head is made of a synthetic resin. However, it is also possible for both parts to be made of steel, or for both to be made of a synthetic resin, in which case they can consist of one piece, for example.